This invention relates to modified strains of Pasteurella multocida for use in poultry vaccines.
It has been more than 100 years since the first fowl cholera vaccine was developed by Pasteur. Since then there have been many attempts at producing both live and inactivated fowl cholera vaccines. Bacterins have been found to induce immunity only to homologous serotypes while avirulent live vaccines provide protection to heterologous serotypes. Since there are many different serotypes of Pasteurella multocida that can lead to fowl cholera in turkeys it would appear to be more advantageous to vaccinate with a live vaccine.
There have been many live fowl cholera vaccines developed since Pasteur. The first successful avirulent live vaccine was the Clemson University strain (CU strain). The CU strain was found to provide both humoral and cell-mediated systemic immunity and protection to the major types of P. multocida infecting turkeys. Although the CU strain stimulates a good immune response in turkeys, it has the disadvantage of resulting in mortality as high as 4% following vaccination.
A number of subsequent Pasteurella multicocida strains have been developed, for example, as described in U.S. Pat. Nos. 4,506,017, 4,388,299, 4,335,106, 4,328,210, 4,293,545, (bovine, porcine and ovine), U.S. Pat. Nos. 3,501,770, 3,526,696 (multi-bacterial vaccines to prevent shipping fever), U.S. Pat. No. 4,136,169 (poultry vaccine made from bacterins), and U.S. Pat. Nos. 4,169,886, 3,855,408 (attenuated poultry vaccines). There remains a need for a safe, effective vaccine providing good humoral and cell-mediated systemic immunity and protection to the major types of P. multocida.
It is therefore an object of the present invention to provide a live P. multocida vaccine for use in immunizing poulty.
It is a further object of the present invention to provide a live P. multocida strain that is an effective immunizing agent but less virulent than the Clemson University strain.